This invention relates to a pyrolytic process for making shaped structures of carbon and silicon carbide, starting with formed precursors having walls made of a resin which is heat-degradable to carbon, and in which is dispersed siliceous material such as pulverized silica or glass which combines when heated with carbon in the resin to form silicon carbide.
This process is especially useful in making a new article of manufacture comprising silicon carbide and carbon macrospheres which are of the order of one half to eleven millimeters in diameter and which are especially useful as fillers in high-temperature composites, and in other applications wherein such characteristics as resistance to high-temperature, wall porosity, and low electrical impedance are important.
This process includes the step of pyrolytic heating which can be done in apparatus of the type disclosed and claimed in Shaver and Leake U.S. Pat. No. 4,279,702. Moreover, the present process resembles the teachings of Shaver and Leake U.S. Pat. No. 4,229,425, as far as the heating and cooling steps are concerned. However, the patented process without changes would not make silicon carbide structures, partly because the steps of the process would not heat the precursors long enough, and partly because the starting material does not contain the necessary ingredients to form silicon carbide.
U.S. Pat. No. 3,673,101 to McKenney et al teaches a process for making metal carbide plus carbon microspheres using ion exchange resin spheres which are externally coated with metal salt and heated to convert the metal salt to a carbide. However in this process, the carbon merely serves as a support and does not take part in the process of forming a carbide.
U.S. Pat. No. 3,264,073 to Schmitt coats phenolic microspheres with a metal, and then heats them in a hydrogen atmosphere to remove the carbon and leave the metal.
A range of degradable materials from which the original precursors can be formed includes polymers of alkyd or phenol resins or polyurethanes, according to an article in Chemical Abstracts, Vol. 73, 1970, page 36, abstract 110,604g.